My co-pending patent application Ser. No. 796,424 describes my stoichiometric burners and presents an expression for the stoichiometric aperture spacing. The stoichiometric spacing equation is exact, provided that the temperatures of the air and gaseous fuels are identical. This however is not the case in oven broilers.
The sole purpose of this application is to develop an equation for the stoichiometric aperture spacing of burners which will operate in a gas broiler whenever the air and gaseous fuel temperatures differ.
The stoichiometric air-to-fuel gas ratio is the most fundamental parameter in determining the stoichiometric aperture spacing. Under the assumption that the temperatures of fuel gas and air are equal, I found that a stoichiometric burner should be constructed to have a gas fed burner chamber with a flat top having a two dimensional array of apertures of diameter d.sub.0 wherein the linear spacing between these apertures should be given by the equation D.sub.s =2.42Rd.sub.0, wherein R is the air-to-gas ratio, representing the relative amount of air entrained by the free turbulent gas jets emerging from these apertures before the jets merge at some distance from the burner plane. For a specific distance D.sub.s, the jets merge when the amount of air that has been entrained is such that R is the stoichiometric air-to-gas ratio as needed for complete combustion. I found that if the spacing is smaller by just a few percentages as compared with the desired value for true stoichiometry, the combustion becomes drastically incomplete. I further found that a spacing D.sub.s being about 15 percent or more larger than the stoichiometric spacing, the air-gas mixture is too diluted for maintaining a temperature sufficient for combustion. Thus, the spacing of the aperture should be as close as feasible to the stoichiometric spacing, permitting roughly a tolerance range from about -1 percent to less than +15 percent.
The stoichiometric ratio is a volumetric ratio. However, the densities of air and gaseous fuels are temperature dependent. The densities of these gases are inversely related to their absolute temperatures. In other words, the product of the densities and Rankine temperatures of the same gas is equal to a constant. The density of air at 70.degree. F. which is 530.degree. F. on the absolute scale, is 0.075 lbs/ft.sup.3. Thus, the arbitrary constant becomes 0.075 .times. 530 = 39.75.
The density of a specific natural gas is 0.0465 lbs/ft.sup.3 at 530.degree. Rankine. Thus, the arbitrary constant for the gaseous fuel is 0.465 .times. 530.degree. = 24.65. Thus, the densities of air and gaseous fuels can be expressed by the following equation, namely: EQU .lambda..sub.A = 39.75 T.sub.R and .lambda..sub.G = 24.65 T.sub.R
where
.lambda..sub.A and .lambda..sub.G are the densities of air and gaseous fuels in units of lbs/ft.sup.3 and T.sub.R is the absolute Rankine temperature.